A light-emitting diode (LED) standard for calibrating a lighting metrology system must first be calibrated for total luminous flux, chromaticity, or other properties and then kept stable. This is generally done via stabilization of the operating current and temperature of the LED. However, this process cannot guarantee stable light output, which may fluctuate during the necessary seasoning process (typically by 5-10% over the first 1,000-2,000 hours of life) and decline during the normal useful life of the LED (typically by 15-30% over ˜50,000 hours). Such variations far exceed the generally acceptable 1-3% level of uncertainty required for calibration standards.
To mitigate these instabilities, users generally season the LED for ˜2,000 hours before using the standard for calibrations. Users may additionally recalibrate the LED after every ˜100 hours of use, which can result in significant development and production delays. Furthermore, the LED generally requires a short period of stabilization after being activated, from several minutes to tens of minutes. While closed-loop active temperature control has attempted to mitigate this problem, the LED is still unusable during this warm-up period, which results in further short-term delays in equipment calibration and general productivity. It may therefore be desirable to accelerate stable operation of the LED in the short term. It may also be desirable to ensure stable long-term operation of the LED while eliminating delays associated with the seasoning and recalibration processes.